The invention relates generally to methods and apparatuses for controlling the trajectory of a spinning projectile. The invention further relates to roll damping apparatuses for controlling the spin of a first section of a spinning projectile relative to a second section using frictional forces, wherein the first and second are rotatably attached about a roll axis of the projectile, and methods for controlling the spin of a first section of a spinning projectile relative to a second section using frictional forces.
In certain military applications, there is a significant need for “smart” projectiles wherein the operator can effectively control the course the projectile takes and the target location that is impacted. Such navigational control requires the ability to impart precise forces to a rapidly spinning projectile with respect to the Earth inertial frame to achieve a desired directional course. Past devices have used arrays of propulsive outlets, fuels and pyrotechnics to produce the necessary forces for the desired two-dimensional course correction. However, these devices suffer from significant disadvantages, such as the danger of premature explosion, and the shock caused by these devices often leads to imprecise course corrections.
Others have attempted to provide two-dimensional course correction in a spinning projectile with a front and rear section. For example, in U.S. Pat. No. 5,452,864, Alford et al. describe a method and apparatus for controlling the roll of a projectile using an electromechanical roll control system. The Alford electromechanical system utilizes an electromagnetic torque created by an armature coil interacting with magnets mounted in the rear section to adjust the spin rate of the front section. However, the reliance on the magnetic forces to slow the sections relative to one another illustrates that the Alford electromechanical system would have to be rather large, and require large amounts of power, to overcome the rotational inertia of the spinning front section to control the roll of the projectile.
Thus, there is a need for a method and apparatus for controlling the spin rate of a two-section, spinning projectile that can control the relative speeds of rotation of the two spinning sections, despin one section relative to the other, maintain a non-rotational state relative to an Earth inertial reference frame, and have the ability to reorient the projectile to a new non-rotational state position. There is a further need for such a method and apparatus that is compact, efficient, robust, easily scalable, requires little power, and avoids the disadvantages of known devices.
Accordingly, the present invention provides a roll damping apparatus, and methods of employing the same to control the spin of a spinning projectile, that overcome the disadvantages of known devices while offering features not present in known devices. Although certain deficiencies in the related art are described in this background discussion and elsewhere, it will be understood that these deficiencies were not necessarily heretofore recognized or known as deficiencies. Furthermore, it will be understood that, to the extent that one or more of the deficiencies described herein may be found in an embodiment of the claimed invention, the presence of such deficiencies does not detract from the novelty or non-obviousness of the invention or remove the embodiment from the scope of the claimed invention.